Is it ensure, insure, or assure?
early 15c., "to pour in, introduce, soak," from Latin infusus, past participle of infundere "to pour into," from in- "in" (see in- (2)) + fundere "pour, spread" (see found (v.2)). Figurative sense of "instill, inspire" first recorded 1520s (infusion in this sense dates from mid-15c.). Related: Infused; infusing.
infuse in·fuse (ĭn-fyoōz')
v. in·fused, in·fus·ing, in·fus·es
To steep or soak without boiling in order to extract soluble elements or active principles.
To introduce a solution into the body through a vein for therapeutic purposes.